B767-332 ACFT CLRED FOR TKOF AND PNF; CAPT; CONFIRMED CLRNC BUT WAS XMITTING ON INTERPHONE SINCE HIS RADIO WAS SET INCORRECTLY. TWR DIDN'T HEAR READBACK AND ISSUED A HOLD CLRNC. REALIZING RPTR ACFT WAS ON TKOF ROLL; TWR HAD ANOTHER ACFT ON APCH GO AROUND.

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OUR ACFT WAS CLRED INTO POS AND HOLD ON RWY 28 IN MSY. WHEN WE WERE STOPPED IN POS; THE CAPT GAVE ME CTL OF THE ACFT; AND HE TOOK THE RADIOS. TWR CLRED US FOR TKOF; AND THE CAPT ACKNOWLEDGED THE CLRNC. I ADVANCED THE THROTTLES TO TKOF PWR AS THE CAPT COMPLETED THE BEFORE TKOF CHKLIST ITEMS (EXTERIOR LIGHTS SET; XPONDER; TCASII SET) AND CALLED THE CHKLIST COMPLETE. WE HEARD A GARBLED RADIO CALL AND HEARD TWR DIRECT ANOTHER ACFT ON FINAL FOR RWY 1 TO GAR. I ASKED THE CAPT TO RECONFIRM OUR TKOF CLRNC WITH TWR. HE CALLED AND ASKED TWR; BUT I DIDN'T HEAR HIM XMIT OVER THE RADIO; JUST INTERPHONE. I CALLED TWR AND ASKED TO RECONFIRM TKOF CLRNC. TWR SAID CONTINUE TKOF (WE WERE ABOUT 100 KIAS NOW); BUT HE HAD EARLIER CANCELED OUR TKOF CLRNC SINCE HE DIDN'T HEAR OUR ORIGINAL ACKNOWLEDGEMENT. THE CAPT THEN REALIZED HE HAD BEEN XMITTING OVER INTERPHONE; WHICH HE HAD USED TO TALK TO THE PUSHBACK CREW. TWR TOLD US THAT HE HAD NO GREAT CONCERN ABOUT THE INCIDENT. THE OTHER AIRPLANE WAS APPARENTLY VULNERABLE TO OUR JETBLAST IF HE WOULD HAVE LANDED AND ROLLED TO THE END. WE NEVER HEARD THE TKOF CLRNC CANCELED BY TWR. THE CAPT AND I REVIEWED THE EVENTS AND AGREED A GOOD TKOF SAFETY CHK SHOULD INCLUDE RADIO SWITCH POS.